Ecological Consequences of Deforestation

The primary ecological consequences of deforestation are decline in biodiversity, invasion of exotic species, destruction of hydrological cycle, increase in water runoff and decrease in water quality, and acceleration of soil erosion. Tropical forests contain between 70% and 90% of all of the world species, and as a result of deforestation the planet is losing between 50 and 130 animal and plant species each day. Deforestation dramatically impacts runoff and hydrological regime, which threatens, for example, about 2000 known species in the waters of the Amazon Basin - 10 times the number found in Europe. Clearing of tropical forests substantially impacts fertility of soil. About 80% of soil in the humid Tropics is acid and infertile. Once the soil temperature exceeds 25 ° C, volatile nutrient ingredients like nitrogen can be lost. Due to intensive rainfalls and soil specifics in the Tropics, a single storm can remove up to 100-1501 topsoil per hectare after deforestation. Deforestation can also decrease the social, esthetic, and spiritual values of forested landscapes. The extent and magnitude of these impacts are influenced by the size, connectivity, shape, context, and heterogeneity of the forest patch remnants. A critical point of negative change in landscape functionality - when fragmentation increased rapidly - on average occurs when mature forest declined to 30-35% of the landscape area.

Forest-cover decline alters regional and potentially global climate system by affecting surface energy, water, and greenhouse gas (GHG) fluxes. Deforestation of temperate and boreal forests has a cooling effect on near-surface climate by increasing surface albedo because cultivated fields generally have a higher surface albedo than natural forests. In tropical regions, deforestation generally leads to the opposite response where the prevailing effect is a decrease ofevapotranspiration due to lower surface roughness and a shallower rooting zone. The associated decrease in the latent heat flux suggests a warming trend. Change of evapotranspiration and sensible heat flux impacts the low-level atmosphere, regional, and, potentially, global-scale atmospheric circulation. For instance, higher rainfall and warmer temperature are already observed due to recent large-scale deforestation in the Amazon Basin. However, the length of the dry season increases due to deforestation-induced rainfall inhibition, which can be accelerated by rainfall reduction in future due to global warming. The changes in forest cover have consequences far beyond the Amazon Basin. Regional-scale deforestation in the Tropics has been observed in a number of modeling results to lead to remote temperature and precipitation changes. Simulations for the twenty-first century give regional anomalies (due to human-induced land-cover change) as ±2 K in magnitude.

There are already recognized impacts of current climate change on tropical forests. Biomass and production of pristine tropical forests is increasing but it expected to be reversed. Climate change and fragmentation substantially increased vulnerability of tropical forests to fire. The species composition is changing even in remote areas. Strong negative relationship is recognized between changes of precipitation regime and net primary productivity (NPP) in the humid Tropics.

Global simulations show a clear decline of vegetation productivity with increasing values of its fraction that is appropriated to human use. This decline is the consequence of two effects: reduction of biomass and climatic differences associated with a reduced vegetation cover. An important biospheric feedback of decreasing biomass is changes in the strengths of dissipative processes in terrestrial ecosystems.

Territories prone to deforestation, degradation, and desertification contain a huge amount of organic carbon:

world tropical forests contain 220-270 PgC in vegetation and 220PgC in soil (down to a depth of 1m); drylands and boreal forests contain, respectively, c. 240PgC and 470PgC in soil. Human-induced land-use-land-cover change (LULCC) destroys the equilibrium state of these carbon pools and eventually impacts stability of the Earth system due to large emissions of major GHGs to the atmosphere because the biomass stock per hectare in standing forest is much higher than in any replacement use, including tree crops and silviculture, and as a result of substantial decrease of soil carbon after the conversion.

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